on the edge The cost of conserving species smear campaign eggs and their bacterial barrier marietjie froneman

cience is only beginning to under- with pits that make up around a third of the Upupa afri- stand some of the mutually beneficial total surface area. When the female smears canus. The se- ways in which birds interact with bac- her uropygial gland secretion onto the egg, cretion smear on their Steria and other denizens of the microscopic these pits become filled, their function ap- eggs provides a barrier against world. A novel symbiotic relationship be- parently being to maximise adhesion of the potentially harmful bacteria. tween bacteria and the secretion to the egg’s surface. warwick tarboton Upupa epops has recently been uncovered Another part of the study involved exper- experimentally curtailed, hatching success by ornithologists and microbiologists from imentally preventing some of the breeding was significantly related to the density of the University of Granada in Spain. females from transferring uropygial gland Enterococcus bacteria in the uropygial gland Hoopoes are well known among orni- secretion to their eggs; the team devised secretion. Likewise, hatching success was re- thologists for the foul-smelling secretion a way to attach a narrow-gauge catheter lated to the amount of these bacteria present that females and nestlings produce from to the uropygial gland and thereby cause on the eggshells. In other words, the symbi- their uropygial (or preen) glands, particu- the secretion to drain into a small plastic otic bacteria in the uropygial gland secretion larly when they are disturbed. There are tube attached to the with an adhesive appeared to directly increase the chances of some intriguing aspects to the breeding bio­ bandage. This manipulation vastly reduced the embryos surviving to hatching. logy of these birds, including the fact that the quantity of secretion present on eggs, These fascinating results reveal that sym- breeding females appear to use their bills to which in turn resulted in far lower densi- biotic bacteria in the hoopoes’ uropygial smear this uropygial gland secretion onto ties of symbiotic bacteria belonging to the gland secretion, which the females transfer their eggs, the function of this behaviour genus Enterococcus, which occur in the to the eggs’ surface, provide the embryos being unclear until now. The researchers, uropygial gland and are hence transferred with protection from disease-causing bac- several of whom have worked extensively to the eggs. In contrast, the density of two teria. This study, in addition to uncover- on hoopoes over the past decade, took a other bac­terial genera, Staphylococcus and ing a novel symbiotic interaction between closer look at this peculiar behaviour. Enterobacteriacea, remained unchanged birds and bacteria, provides the answer to Working at a site in southern Spain where compared to the eggs of females that had an intriguing aspect of the hoopoes’ breed- hoopoes and several other species breed in unrestricted access to their uropygial gland. ing biology. nest boxes, they elucidated the significance Members of these two last-mentioned ANDREW McKECHNIE of the secretion using several complement­ bacterial genera are well-known pathogens ary approaches. One involved com­paring and sources of mortality for avian embryos, Reference: Martín-Vivaldi, M. et al. 2014. the outer surfaces of hoopoe eggs with those and the most intriguing result of the study ‘Special structures of hoopoe eggshells en- of the eggs laid by scops owls, rollers, star- emerged when the researchers examined hance the adhesion of symbiont-carrying lings, doves and sparrows. The surface of correlations between bacterial densities and uropygial secretion that increase hatching hoopoe eggs, they discovered, is not smooth hatching success. Among females whose success.’ Journal of Ecology 83: like that of other species, but densely covered access to their uropygial gland was not 1289‒1301.

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